The present invention relates to intracranial pressure relief valves and, more particularly, to a position sensor for non-invasively sensing the position of a magnetic wrench in a non-invasively adjustable intracranial pressure relief valve.
Hydrocephalus is a condition in which the body, for any one of a variety of reasons, is unable to relieve itself of excess cerebrospinal fluid (CSF). The collection of excess CSF in the ventricular spaces of the brain results in an increase of both epidural and intradural pressures which, in turn, causes a number of adverse physiological effects, including compression of brain tissue, impairment of blood flow in the brain tissue and impairment of the brain's normal metabolism.
Treatment of a hydrocephallic condition frequently involves relieving the accompanying abnormally high intracranial pressure. A variety of CSF pressure regulator valves and methods for controlling CSF pressure have been developed which include various forms of check valves, servo valves or combinations thereof. Generally, such valves serve to divert CSF from the ventricles of the brain through a discharge line to some suitable drainage area of the body such as the veinous system or the peritineal cavity. Both check valves and servo valves operate to avoid the development of abnormally high intracranial pressures, and preferably serve to maintain such pressures within limits which vary according to the specific requirements of individual patients. Accordingly, CSF pressure relief valves frequently include various forms of mechanisms which permit the pressure-flow characteristics of the valve to be adjusted as necessary to suit the needs of particular patients.
In one CSF relief valve, as disclosed in co-pending application Ser. No. 467,326, filed Feb. 17, 1983 by the present inventor, a diaphragm containing a valve seat is positioned in a valve casing, and both sides of the diaphragm are exposed to the CSF fluid. A ball-shaped valve closure member is mounted to a threaded screw member in the casing so as to engage the valve seat. The force by which the closure member engages the valve seat, and thus the pressure differential at which the valve permits CSF fluid flow, can be adjusted by threading the screw member in or out prior to implantation of the valve within a patient.
It frequently develops however, that optimum performance of the valve may be obtained at an adjustment setting other than that to which the valve was set at the time of implantation. Once implanted, readjustment of the valve would require invasive surgery and hence would be justified only in the case of gross misadjustment.
To permit simple readjustment of implanted CSF pressure relief valves, non-invasively adjustable valves have been developed. Once such valve is that disclosed in co-pending application of the present inventor Ser. No. 515,700, filed July 21, 1983, in which a rotatable magnetic element or wrench is coupled to a threaded screw member within the valve. By bringing a specially constructed magnetic tool into the vicinity of the implanted valve, magnetic communication is established between the tool and the magnetic wrench to permit a physician to rotate the wrench and thereby alter the pressure-flow characteristics of the implanted valve. Since magnetic coupling between the tool and the wrench is employed, a completely non-invasively adjustable valve is provided.
To permit a physician to determine the relative adjustment setting of such an implanted, magnetically adjustable valve, it is necessary that a complete and accurate record of the initial valve setting, together with any subsequent readjustments thereof, be maintained. This places an increased burden on health care personnel and creates the risk that accurate knowledge of the valve adjustment setting might be inadvertently lost.
The present invention concerns a CSF valve system wherein a non-invasive position sensor and indicator are provided for indicating the relative adjustment setting of the implanted valve. The valve position sensor includes a pivotally mounted magnetic indicator member which can be placed in the vicinity of an implanted valve. The magnetic field produced by the magnetic wrench causes the pivotable magnetic member to rotate to a position aligned with the magnetic field lines. An indexing mechanism assures that the position sensor is located in the same position relative to the valve during each measurement of the magnetic wrench position. Accordingly, the position of the magnetic indicator member will vary in accordance with the setting of the implanted valve. This permits health care personnel to quickly, accurately and non-invasively ascertain the relative adjustment setting of the implanted valve whenever necessary.
Accordingly, it is an object of the present invention to provide a magnetically adjustable CSF pressure relief valve system having an indicator for indicating the relative adjustment setting of the implanted valve.
It is a more specific object of the present invention to provide a position sensor for non-invasively indicating the relative adjustment setting of a magnetically adjustable CSF pressure relief valve.